There are believed to be methods for operating an electrical network in a motor vehicle. Especially in the ever more popular hybrid drive devices of motor vehicle, which have at least one electric machine and one internal combustion engine as drive units, a multitude of methods for operating the associated electrical networks are believed to be available. In this connection it is important to set the network voltage of the network so as to provide a sufficient network voltage to all of the loads electrically connected to the network. Since comparatively high voltages must be provided in hybrid motor vehicles in order to be able to use the electric machine as a motor to drive the motor vehicle, methods are known for protecting the electrical network and the components electrically connected to the electrical network, which prevent damage. Thus the inverter controlling the electric machine has an overvoltage protection for example, which switches the inverter into a short-circuit operating mode when a specifiable voltage limit of a network voltage is exceeded, that is, when the network voltage exceeds a specifiable voltage limit.
In addition, it is believed to be understood to disconnect the electrical accumulator electrically from the network when a malfunction, for example of the electrical accumulator, is detected. If the electric machine is operating as a generator at this time, this has the consequence that, by “discarding” the electrical accumulator, the network voltage increases greatly and thus exceeds the specifiable limit voltage of the inverter, whereupon the inverter is switched to the short-circuit operating mode. Since now neither the electrical accumulator nor the electric machine feed power into the network or provide a voltage, the voltage existing in the network, for example of an intermediate circuit capacitor, is quickly reduced until the electrical network breaks down electrically and no network voltage or no usable network voltage remains. If high-voltage loads are connected to the network and are activated, the network accordingly breaks down more quickly. Since now there exists no more network voltage, it is also no longer possible to operate/regulate the electric machine as a generator. The entire system fails.